Outdoor navigation is widely deployed through the use of various global-navigation-satellite-systems (GNSS) such as the U.S. Global Positioning System (GPS), the Russian Global Navigation Satellite System (GLONASS), and the European GAL/LEO. These systems may operate effectively outdoors but, due to satellite reception problems, may not be very effective indoors.
Relatively recently, there has been a focus on solving indoor navigation problems. One solution may be based on Time-of-Flight (ToF) methods. Time-of-Flight may be defined as the overall time a signal propagates from a mobile communication station (e.g., user) to an access point (AP) and back to the user. This value may then be converted into distance by dividing the time by two and multiplying the result by the speed of light. This method may be robust and scalable but may require hardware changes to the Wi-Fi modem.
There are general needs for performing indoor navigation out of range of the GNSS.